Packet Data System Design Issues
Link adaptation, downlink multiplexing & dynamic uplink allocation
- Multiple code rates and modulation schemes to match with the link condition of individual UT.
- Certain information has to be shared with and read by all the UTs attached to the channel regardless of the individual link margin.
- Modulation and coding scheme has to be known prior to demodulating and decoding the payload.
- USF has to be transmitted to all the UTs every burst.
- Solution: physical layer header.
- p/4-QPSK modulation and Golay code regardless of the modulation and coding scheme used in the payload.
Smart spot beam allocation
- Dark beam concept allows illuminating coverage area only when needed (actual traffic exists). Allows carriers to share resources.
- A-BCCH, T-BCCH
- GBCCH (EGMPRS)